Power Meters

Power meters include the W5USJ 4-port directional coupler bridge with a modified Accuprobe used as a diode compensated meter amplifier.
Also shown here is my rendition of the KD1JV digital power meter from 4SQRP.

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Download SMT RF Probe Drawing and Artwork here — SMT RF Probe Drawing PDF

W5USJ Watt Meter The finished Watt meter is housed in an LMB 136-P enclosure. The project includes a 4-port 20dB coupler and a modified Accuprobe kit from NorTex. The kit is modified to provide a diode compensated amp similar to that used with the OHR WM-2. Scroll down to see the modified Accuprobe circuit schematic. W5USJ Wattmeter
Internal Workings Here's the inside of the meter. The 20dB directional coupler is on the left. The modified Accuprobe diode compensated amplifier is on the right. The 3 calibration pots are mounted Manhatten style. Calibration was found to be very close to the meter scale markings. The schematic shows 7 turns used with the toroids. To get 20dB coupling/isolation, 10 turns were used in the finished unit. Also, the faraday shield was not used.

Accuprobe Kit Modified This is the Accuprobe kit modified for use as the diode compensated meter amplifier. The kit was designed and used with permission here by the NJQRP club’s Joe Everhart, N2CX. It is being sold through AmQRP by the NorTex QRP club.

Use of the Accuprobe provided an easily modified circuit for the meter amplifier. The modifications shown in the schematic provide a circuit much like that used in the OHR WM-2.
Dip Pins

Digi Power Meter
KD1JV Digi Power Meter Kit assembled prior to testing and mounting in an enclosure. Kit sold by 4SQRP club.

Two weeks before George, W5YR, died, I'd taken my FT-817 to his place and calibrated the power against his 0.5% HP power meter. The 817 was used for calibration of the digi meter.
Digi Power Meter Kit
Digi Power Meter Power meter kit installed in an LMB Crown Royal enclosure. To provide plenty of room, I used the same CR-531 used for the NoGaWatt meter. Visibility for the LEDs is provided through openings cut into the cover.

The rechargeable battery pack provides 4.5 to 5 Volts for the digi meter. I used a gimmick to isolate the on-board batteries. Function pushbuttons are wired in parallel.


W5USJ Power Meter Modification Schematic

Powermeter Schematic


20dB 20Watt Power Attenuator

Powermeter Schematic